Hi, as proposed here it's now possible to change the color of the background. The background basically persists out of a tile frame that's drawn over and over again. Unfortunately it's a bit less simple, as there are some special cases due to elevated coast lines. As a result you have to provide 3 frames to override the background:

frames_explain.png (1.95 KiB) Viewed 896 times

Frames b and c are used to draw the background above water at the edges. This is crucial as ocean is drawn everywhere and has to be overdrawn at the correct positions.